1. Field of the Invention
The present invention relates generally to scattering devices that reflect electromagnetic signals. More particularly, the present invention relates to an apparatus which enhances the performance of scattering devices by increasing the amplitude of the time variations in a reflected signal which includes information such an identification code.
2. Description of the Prior Art
In the past conventional scattering devices consisted generally of a plurality of single strand dipole elements. Examples of conventional scattering devices include chaff, reflector beacons used on aircraft, and corner reflectors used on boats and by hikers. Conventional scattering devices such as chaff, decoys and reflector beacons that receive an incident electro-magnetic signal, reflect a constant amplitude signal with time.
State of the art missile seekers are capable of distinguishing between chaff from a moving aircraft by utilizing Doppler rejection algorithms. The Doppler rejection algorithms are capable of distinguishing chaff from moving aircraft because of the significant reduction in chaff velocity when compared to the velocity of a moving aircraft.
Static reflectors used on boats, bicycles and individuals who are, for example, runners wearing reflectors generate static reflection signals that may not be identifiable from clutter background reflections. Static reflectors generally do not include a method for identification of the person or vessel to which the reflector is attached.
Current approaches to radio frequency tagging lack adequate modulation signal strength to be used at long range, for example, several miles or in a cluttered environment.
Further, currently calibration devices used for Doppler reflection test, such as jet engine modulation, lack the dynamic range that would produce high quality test results.
Accordingly, there is a need for an apparatus for varying the reflection properties of scattering objects such as missile decoys, chaffs and towed decoys, rescue beacons, reflectors, antennas and the like. By varying the reflection properties of a scattering object, a threat missile will be less likely to distinguish a moving target, such an aircraft, from the scattering object which may be chaff or a decoy.
In addition, there is a need for a means to provide an identification code with the signal reflected from the scattering object.
The present invention comprises a scattering object, which may be, for example, an antenna, a load impedance which is optimal and a switch which connects the scattering object to the load impedance. The scattering object includes fundamental scattering characteristics, referred to as structural scattering, which arise from surface currents induced by an incident electro-magnetic or radio frequency signal. The optimal load impedance is an electrical device, such as inductor, that produces a current at the connection between the scattering object and the load impedance that has a phase and amplitude which result in a minimal scattered signal. By using the switch to switch the load impedance in and out of the connection with the scattering object a large dynamic range for a fluctuating scattered signal may be achieved.
The switch may be an electrical RF switch, a gravity operated switch, a chemical induced operating switch or a photonic switch. When an electrical RF switch has a digital processor connected thereto, the switch may be used to provide a digital identification code to the scattering object which is then transmitted by the scattering to a receiving antenna.